Temporal variations of acid rain based on the records of precipitation analyses at Nishigara, Tokyo, for 1913-1940

Abstract

Wet depositions of acid rain including ammonium, nitrate, and non-seasalt sulfate have an important effect on precipitation pH. The author has collected data sets of past precipitation analyses to study the historical change in acid rain. The ministry equivalent to the current Ministry of Agriculture. Forestry and Fisheries started the measurements of precipitation components and atmospheric nitrogen at Nishigahara, Tokyo in 1913, and continued until 1940. Monthly reports were used to investigate the contribution of nitrogen in precipitation to plants. This study assesses wet depositions of ammonium, nitrate, and non-seasalt sulfate from these data sets. Wet deposition should be estimated only from rain, and the precipitation collector must be protected from dry deposition. In the precipitation analyses at Nishigahara for 1913-1940, the precipitation collector was set up in the field whether rain or not. This suggests that depositions of rain included some dry depositions. The author estimates the wet deposition for each ion at Nishigahara by assuming conversion ratios for the wet depositions. For ammonium ion, wet depositions at Central Meteorological Observatory are used for that at Nishigahara because there were no significant differences in the wet depositions between Central Meteorological Observatory and Takinogawa, which is at nearly the same location as Nishigahara.